A NUMERICAL ABSORBING BOUNDARY-CONDITION FOR 3D EDGE-BASED FINITE-ELEMENT ANALYSIS OF VERY LOW-FREQUENCY FIELDS

The numerical absorbing boundary condition (NABC) approach in conjunct ion with the three-dimensional edge-based formulation of the finite-el ement method (FEM) is applied to the problem of very low frequency (VL F) electromagnetic radiation and scattering. The key step in the NABC approach is to derive linear relationships that link the values of the field along the boundary edges to those at the neighboring ones. Deri ved via a robust SVD-based scheme, these linear relationships are sati sfied to within a certain tolerance, by all of the outgoing wave compo nents. They can thus be used in lieu of the FEM equations employing th e usual absorbing boundary conditions for the boundary edges. Although the NABC approach provides a simple way to derive an accurate local b oundary condition for mesh truncation at an arbitrary frequency, it ap pears to be the only viable absorbing boundary condition at VLF, becau se the conventional absorbing boundary conditions are almost as reflec ting as perfectly conducting magnetic walls at these frequencies. (C) 1995 John Wiley & Sons, Inc.